Plastic materials are often used as containers for beverages and, for carbonated beverages, the plastic material forms a barrier against permeation of the gas, e.g. carbon dioxide, which provides the carbonation. A reduction of the carbon dioxide permeation rate helps to maintain a high level of carbonation in the carbonated beverages. Therefore, the choice of suitable plastic material, the distribution of the material, and the processing conditions are important factors in producing such plastic containers. One major difficulty with volume production of plastic containers is that periodic sampling of production containers is required to ensure that the container is performing to the desired specifications and containing carbon dioxide as desired.
Originally, the periodic sampling of plastic containers required actual, direct measurement of the carbon dioxide in the container. This was complex and required large test equipment, including plumbing and precision gas detectors, to destructively test the plastic containers. In addition, since the decrease over time in carbonation level in a sealed container may be slight, a test cycle would usually last for several weeks before an estimate of carbonation loss rate could be obtained for predicting the shelf life of a carbonated beverage.
Non-destructive carbon dioxide testing systems, which allow for more rapid testing of plastic containers during production, have been developed. One such system is described in U.S. Pat. No. 5,614,718, which requires the creation of a prediction model using one or more analysis containers. The analysis containers are subjected to spectral analysis using near infrared (NIR) transmission to acquire spectral signatures from the one or more containers. The containers are also physically measured to obtain the dimensions which are then stored as calibration data. From the spectral analysis and the calibration data, prediction models are created and then used to non-invasively test production containers filled with carbonated beverages to predict carbonation retention and shelf-life. The non-invasive testing of production containers involves transmitting NIR energy through the production container and measuring the received NIR energy. Using the received energy and the prediction model, carbonation retention may be determined.
This non-destructive test system reduces carbon dioxide retention test times from several weeks, as described above with the destructive testing, to minutes or less. However, a new prediction model is required for each new container type to be tested. Moreover, this system is suitable for use in a carbonated beverage facility and not for field testing carbonation levels of carbonated beverages on the shelf in stores or in inventory.
Therefore, there is a need for a smaller and simpler non-destructive carbonation concentration analyzer which may more rapidly test for carbon dioxide concentration in the field in a variety of transparent or semi-transparent containers without the need for predetermined prediction models, such as described in U.S. Pat. No. 5,614,718.